Mixer on the pencil tubes may be made on one- grid or two grid schematic.
At the one- grid schematic both input RF signal and RF- voltage
from a heterodyne oscillator come on to the first grid of the
tube. Voltage from a heterodyne oscillator should not be exceed
1.5- 2.0 – V or side channels may be appeared. Two- grid mixer
works more stable the one –grid one. Figure
2 shows a typical schematic of a two- grid mixer on
a pencil tube. Input RF- voltage goes to the first grid and Voltage
from a heterodyne oscillator goes to the third grid. Voltage from
a heterodyne oscillator should not be less the 12- 15- V. Practically
any pencil tubes may work like a mixer. Such mixers- one and two-
grid, may work up to VHF- Frequencies.
Figure 2 Two- Grid Mixer on a Pencil
Pencil tubes may work at any common schematic of the RF- oscillator where
usual tubes are used. Practically any type of pencil tubes may
work in RF Oscillator.
As usual a Colpitts oscillator is used at the
VHF- band for producing RF- Frequencies up to 300- MHz.
4 shows Typical Schematic of a Colpitts
Oscillator. For stable
work the tank L1C1 is tuned to the frequency twice below that
LkC8 is tuned.
Figure 4 Typical Schematic of a
Colpitts Oscillator on a Pencil Tube